The flow of escaping water was blocked.
Residents of the Granite Creek area told
us that the lodge had been in continuous use
for more than 30 years. Generations of bea
vers kept adding mud, gathered from the bot
tom of the pond, to the upstream dam wall.
Now it rose four feet above the bottom and
was ten feet thick at the base, making it im
pervious to the pressure of water impounded
in the pond.
A network of canals reached out from the
pond (following pages). Dug to extend the
animals' food-gathering range, the outward
flowing canals were at least two feet wide
and as much as three feet deep. Because of
the sloping ground, the system had a series of
locks, each about two feet high, to link upper
and lower sections of each waterway. Across
the middle of every banked-earth lock, the
beavers had made a mud slide that served
as a ramp. On reaching a lock, a beaver
would climb the mud slide, willow branch
in its mouth, and slip into the water of the
upper canal.
A beaver can swim more than 700 feet
along this canal system to reach the main
beaver pond, coming out of the water briefly
only when crossing locks.
Nimble Feet Speed Dining Time
One day in early fall we watched a beaver
swim ashore and walk to a nearby clump of
willows. Standing on its hind feet, broad tail
serving as a prop, it cautiously sniffed the
air; fortunately, we were downwind. It soon
dropped onto all fours to snip off three willow
stems with its sharp teeth.
Gripping the base of each stem firmly in its
mouth, the animal ambled back to the safety
of the pond and commenced its meal in the
shallows. Using front feet as dexterously as
we would use fingers to eat corn on the cob,
the beaver held up foot-long sections of
willow and nibbled the leaves one after the
other. Then it devoured the bark with zest,
turning the stick as it ate.
In spring beavers that have dined all win
ter from their underwater cupboard enjoy a
change of diet: grass, herbs, leaves, buds,
and shoots.
Like other rodents, beavers have four
large, curved incisor teeth. They are bright
orange on the front surfaces; they grow
throughout life and are self-sharpening-the
lower pair works against the upper. Thus
equipped, beavers cut through tree trunks
with surprising speed. Two protective flaps
of skin close off the mouth behind these
chisel-edged incisors, keeping wood chips
and water out of the animal's throat as it
works below the pond surface.
We marveled to see a beaver bite through a
submerged 21/ 2-inch-thick aspen branch in
less than 30 seconds. It then towed this big
branch toward the lodge, only to stop swim
ming halfway there and snip it in two to
lighten the load.
But do not believe those tales that beavers
are expert lumberjacks, capable of felling a
tree in any direction they desire. Many times
we have come upon large trees beavers had
cut that had ended up hanging uselessly in
other trees. A beaver circles a tree as it cuts
out chips; the tree falls on the side with the
heaviest branches. Very often this is toward
a nearby pond, where abundant sunlight
produces the most growth.
Along the Snake River in Wyoming we
found large cottonwood trees, 28 inches in
diameter, cut down by beavers. But other
standing trees nearby bore weathered tooth
marks where beavers had ringed them six
inches deep and then given up the effort.
For reasons yet unknown, beavers oc
casionally abandon trees before they're
felled, and apparently never return to finish
the job. Perhaps they are frightened off by
predators-coyotes sometimes surprise and
kill them-but they have few other enemies
because of their watery environment.
Tough Part Comes After Tree Is Down
Tree felling is only the beginning of the
beaver's work. The animal then must cut
the tree into manageable lengths for trans
porting to the pond. It leaves telltale signs
of its labor.
In the White Mountains of Arizona we
came upon several neat heaps of chips,
arranged in a straight line from an aspen
stump. The three-foot spaces between piles
indicated the length of the logs that the
beaver had dragged to the pond.
Once a branch or log reaches the water, a
beaver easily tows the freight across the pond.
I had the good fortune to view this cargo
shipment from underwater. The beaver's
broad, paddle-shaped tail serves as a rudder,
enabling it to steer a straight course.
Beavers are completely at home in the
water. If danger threatens, they can remain
submerged as long as 15 minutes, thanks to
Beavers, Nature's Aquatic Engineers
723